Check the status of your Race Glaze Refillable Water Filter with this simple dip-in Electronic TDS water hardness meter. The water meter will provide a single reading of parts per million (ppm) dissolved solids. Regular checks will save a potential walk away from your car to return with it covered in water spots. Once the reading rises to 10 or so you will need to replace resin, as it will rise to 20 or 30ppm then rocket to hundreds of ppm, even higher than your tap water, as the resin media releases stored minerals. Simply press the On button and dip into a carefully cleaned receptacle that has been thoroughly rinsed with the water to be tested – a ‘clean’ glass from your dishwasher etc will be contaminated and give a false reading. 12 month guarantee. Instructions included in leatherette pouch.